1. Field of Invention
The present invention is directed to an apparatus for detecting saturation of water in soil.
2. Prior Art
In the field, when it rains, water enters soil. When water content in soil reaches saturation, soil tends to liquidate and collapse, thus causing landslide that could claim precious lives and properties. People have been working hard to prevent landslide. However, landslide occurs as a result of disastrous development of land in some cases, or is simply in God""s hands in some other cases. For whatever cause it may be, landslide is not something that we can completely prevent. Yet, we hope that we can minimize loss of precious lives and properties by evacuation of people and their properties before landslide happens. To this end, people need a warning system.
Warning of landslide may be done by evaluation. Such evaluation is based on precipitation instead of water content in soil, since water content in soil is related to how big and how long the rain falls in an un-sheltered area. When and in what scale landslide may happen is predicted via calculation of precipitation. Such evaluation is simple, however it cannot predict precisely since it does not take into account factors related to terrain and geography.
In fact, landslide is more directly related to water content in soil than to precipitation. Saturation of water in soil can be deemed an omen of landslide, and accuracy for warning of landslide can be improved if apparatuses can be installed to monitor water contents in soil in various positions.
U.S. Pat. No. 4,801,865 discloses a moisture sensor for sensing water content in soil. It provides a reading that varies as water content in soil varies. The reading and the water content are in a linear relation when the water content is in a range of 50xcx9c90% of saturation. However, the reading stops changing linearly with respect to the water content soon after the water content rises over 90% of saturation. In fact, the reading almost comes to a complete stop after the water content rises over 99% of saturation. In this phase, it is difficult to know if the water content really stops rising or continues to rise. This does not cause any serious problem when the moisture sensor is used for irrigation, because it does not matter to stop watering a little bit sooner or later than 100% of saturation. However, this can cause a serious problem if the moisture sensor is used for warning of landslide, for both pre-mature warning and late warning are not desirable.
U.S. Pat. No. 4,959,639 teaches a device for detecting a fluid. Such a device includes a rod, a sleeve and a spring. The rod is inserted in the sleeve, and they are dimensioned so as to allow longitudinal movement relative to each other. A bottom end of the rod is affixed with the bottom end of the sleeve. A spring is also received in the sleeve. A top end of the spring is affixed with a top end of the sleeve while a bottom end of the spring abuts a top end of the rod. Thus, the sleeve is always loaded with tension. The sleeve is made of a material that loses its tensile strength when exposed to the liquid, thus allowing longitudinal movement of the top end thereof relative to the top end of the rod. A detection member is used to detect such a relative movement. Such a device can monitor presence of water; however, it cannot be used as a warning device for landslide for failing to distinguish the status of having some water from the status of saturation reached.
U.S. Pat. No. 4,531,087 discloses a sensor for monitoring moisture in soil by measuring conductivity between electrodes. In such a sensor, two electrodes are spaced apart and packed in a porous medium, protected by a filter medium that excludes particulates but passes moisture. The conductivity of the porous medium between the electrodes is measured to reflect water content in the porous medium. The conductivity is not a strictly linear function of water content in soil. Still, properly interpreted, it can provide valuable information regarding water content at some depth in soil. Simplistically stated, when the porous region is completely dry, there is no or minimal conductivity. A very low or no meter reading will result if current is measured. When the sensor is fully wetted, the conductivity will be at a maximum, and there will be a higher meter reading. To be economically practical, a sensor must work well in a wide variety of soils and be responsive to a wide variety of waters. However, no matter how wet the sensor would be with distilled water, for example, there would always be a low or no reading because conductivity of such water is very low. In dealing with some sorts of liquid, such a sensor may not work at all. Even it works in other sorts of liquid, it cannot distinguish the status of having water from the status of saturation reached since the conductivity does not vary sharply together with water content in soil. Therefore, such a sensor cannot be used as a good device for warning of landslide.
U.S. Pat. No. 5,179,347 discloses a sensor for sensing moisture in soil. Such a sensor includes a metal housing with a wall defining an internal cavity. A number of apertures are defined through the wall. A porous filter liner is received in the cavity, thus lining the wall. A granular transfer matrix with silica sand is received in the linear. A buffer tablet of compacted gypsum abuts the transfer matrix. An electrode matrix including silica sand abuts the buffer tablet. Two electrodes contact the electrode matrix. The electrodes are spaced apart from each other, and are bridged by the electrode matrix. A lead extends from each of the electrodes. The sensor is closed against entry of moisture from soil in contact therewith except through the apertures that allow the moisture to penetrate the liner and the transfer matrix and pass through the tablet. The moisture dissolves some electrolyte as it penetrates. The moisture further enters the electrode matrix so as to form an electrically conductive path between the electrodes. The conductivity or lack of conductivity of the electrode matrix between the electrodes is indicative of the presence or absence of moisture in the soil. Such a sensor can be used to monitor water content in soil. However, it cannot distinguish the status of having water from the status of saturation reached since the conductivity does not vary sharply together with water content in soil. Moreover, the buffer tablet will be consumed after such a sensor is used for some time, and then cannot work in some sorts of liquid. Such a sensor therefore cannot be used as a good device for warning of landslide.
U.S. Pat. No. 5,969,620 discloses a moisture monitor including a housing, an upper electrode, a lower electrode and a common electrode. The electrodes are all attached to the housing. In use, the housing is inserted in the ground or immersed in the water. As discussed in relation to Table 2, when none of the upper and lower electrodes contacts water, no alarm is provided, for assuming that the moisture monitor is not in use. When the upper and lower electrodes both contact water, no alarm is provided for interpreting that water level is high enough. Only when the lower electrode contacts water while the upper electrode does not, an alarm is provided for interpreting that the moisture is in use and water level is too low. Such a moisture obviously cannot be used to warn of landslide for it is designed to provide an alarm only when water level is too low, not too high.
Therefore, the present invention is intended to obviate or at least alleviate the problems encountered in the prior art.
It is an objective of the present invention to provide an apparatus for precisely detecting saturation of water in soil.
It is another objective of the present invention to provide a durable, accurate apparatus for detecting saturation of water in soil.
To achieve the above-mentioned and other objectives, there is provided an apparatus for detecting saturation of water in soil including a housing including a lower section adapted for insertion in soil, means for permitting water into the housing while blocking soil, a sensor unit received in the housing for sending a signal when water level reaches a pre-determined position, and a control unit for receiving the signal from the sensor unit and for processing the signal.
In another aspect of the present invention, an apparatus for detecting saturation of water in soil includes a housing including a lower section adapted for insertion in soil. A filter is used to permit water into the housing while blocking soil. A sensor unit includes lower and upper reed switches received in the housing, a float for floating on the water in the housing, thus performing as an indicator of the water level, and a magnet attached to the float so that the lower reed switch can detect the magnet and send a signal and that the upper reed switch can detect the magnet and send a signal. A control unit is used to receive the signals from the reed switches, and to divide the distance between the reed switches by the time difference between the signals so as to determine a rate of rising of the water level, and to provide an alarm if the rate reaches a pre-determined value.